Serum interleukin-6 in renal osteodystrophy: Relationship with serum PTH and bone remodeling markers

Interleukin-6, synthesized by osteoblasts in response to PTH, stimulates os teoclastogenesis and bone resorption in vitro, and it has been implicated i n the pathogenesis of bone loss in several clinical situations. The aim of this study was to evaluate whether serum levels of interleukin-6 were incre ased in patients with renal osteodystrophy, and to investigate the possible relationships between serum interleukin-6 and PTH levels on one hand, and serum interleukin-6 and bone remodeling markers on the other. Serum interle ukin-6 (IL-6), intact PTH, osteocalcin, bone alkaline phosphatase (BAP) and carboxyterminal telopeptide of Type 1 collagen (ICTP) were measured in 86 uremic patients. IL-6 (median [range] 16.5 [1.0-430] pg/ml), PTH (279.8 [11 -2004] pg/ml), osteocalcin (143.8 [8-921] ng/ml), BAP (20.9 [6-169] U/l) an d ICTP (38.8 [1.5-181.5] mu g/l) were higher than normal. IL-6 levels corre lated with PTH (r = 0.22, p = 0.04) and with ICTP (r = 0.31, p = 0.004). A stronger correlation was found between PTH and circulating bone remodeling markers (r = 0.66 for osteocalcin, r = 0.56 for BAP, and r = 0.39 for ICTP) . The correlation between PTH and IL-6 was stronger in those patients (n = 15) with severe secondary hyperparathyroidism (r = 0,71, p = 0.003). On the other hand, in the group of patients (n = 41) with PTH lower than 250 pg/m l, there was no correlation between IL-6 and PTH, while IL-6 correlated wit h ICTP (r = 0.44, p = 0.006). Serum IL-6 correlates with ICTP which suggest s that it may mediate bone resorption in renal osteodystrophy.